misc/chattr.1.in

   1 .\" -*- nroff -*-
   2 .TH CHATTR 1 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
   3 .SH NAME
   4 chattr \- change file attributes on a Linux file system
   5 .SH SYNOPSIS
   6 .B chattr
   7 [
   8 .B \-RVf
   9 ]
  10 [
  11 .B \-v
  12 .I version
  13 ]
  14 [
  15 .I mode
  16 ]
  17 .I files...
  18 .SH DESCRIPTION
  19 .B chattr
  20 changes the file attributes on a Linux file system.
  21 .PP
  22 The format of a symbolic mode is +-=[aAcCdDeijsStTu].
  23 .PP
  24 The operator '+' causes the selected attributes to be added to the
  25 existing attributes of the files; '-' causes them to be removed; and '='
  26 causes them to be the only attributes that the files have.
  27 .PP
  28 The letters 'aAcCdDeijsStTu' select the new attributes for the files:
  29 append only (a),
  30 no atime updates (A),
  31 compressed (c),
  32 no copy on write (C),
  33 no dump (d),
  34 synchronous directory updates (D),
  35 extent format (e),
  36 immutable (i),
  37 data journalling (j),
  38 secure deletion (s),
  39 synchronous updates (S),
  40 no tail-merging (t),
  41 top of directory hierarchy (T),
  42 and undeletable (u).
  43 .PP
  44 The following attributes are read-only, and may be listed by
  45 .BR lsattr (1)
  46 but not modified by chattr:
  47 compression error (E),
  48 huge file (h),
  49 indexed directory (I),
  50 inline data (N),
  51 compression raw access (X),
  52 and compressed dirty file (Z).
  53 .PP
  54 Not all flags are supported or utilized by all filesystems; refer to
  55 filesystem-specific man pages such as
  56 .BR btrfs (5),
  57 .BR ext4 (5),
  58 and
  59 .BR xfs (5)
  60 for more filesystem-specific details.
  61 .SH OPTIONS
  62 .TP
  63 .B \-R
  64 Recursively change attributes of directories and their contents.
  65 .TP
  66 .B \-V
  67 Be verbose with chattr's output and print the program version.
  68 .TP
  69 .B \-f
  70 Suppress most error messages.
  71 .TP
  72 .BI \-v " version"
  73 Set the file's version/generation number.
  74 .SH ATTRIBUTES
  75 A file with the 'a' attribute set can only be open in append mode for writing.
  76 Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE
  77 capability can set or clear this attribute.
  78 .PP
  79 When a file with the 'A' attribute set is accessed, its atime record is
  80 not modified.  This avoids a certain amount of disk I/O for laptop
  81 systems.
  82 .PP
  83 A file with the 'c' attribute set is automatically compressed on the disk
  84 by the kernel.  A read from this file returns uncompressed data.  A write to
  85 this file compresses data before storing them on the disk.  Note: please
  86 make sure to read the bugs and limitations section at the end of this
  87 document.
  88 .PP
  89 A file with the 'C' attribute set will not be subject to copy-on-write
  90 updates.  This flag is only supported on file systems which perform
  91 copy-on-write.  (Note: For btrfs, the 'C' flag should be
  92 set on new or empty files.  If it is set on a file which already has
  93 data blocks, it is undefined when the blocks assigned to the file will
  94 be fully stable.  If the 'C' flag is set on a directory, it will have no
  95 effect on the directory, but new files created in that directory will
  96 the No_COW attribute.)
  97 .PP
  98 A file with the 'd' attribute set is not candidate for backup when the
  99 .BR dump (8)
 100 program is run.
 101 .PP
 102 When a directory with the 'D' attribute set is modified,
 103 the changes are written synchronously on the disk; this is equivalent to
 104 the 'dirsync' mount option applied to a subset of the files.
 105 .PP
 106 The 'e' attribute indicates that the file is using extents for mapping
 107 the blocks on disk.  It may not be removed using
 108 .BR chattr (1).
 109 .PP
 110 The 'E' attribute is used by the experimental encryption patches to
 111 indicate that the file has been encrypted.  It may not be
 112 set or reset using
 113 .BR chattr (1),
 114 although it can be displayed by
 115 .BR lsattr (1).
 116 .PP
 117 The 'h' attribute indicates the file is storing its blocks in units of the
 118 filesystem blocksize instead of in units of sectors, and means that the file
 119 is (or at one time was) larger than 2TB.  It may not be set or reset using
 120 .BR chattr (1),
 121 although it can be displayed by
 122 .BR lsattr (1).
 123 .PP
 124 A file with the 'i' attribute cannot be modified: it cannot be deleted or
 125 renamed, no link can be created to this file and no data can be written
 126 to the file.  Only the superuser or a process possessing the
 127 CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
 128 .PP
 129 The 'I' attribute is used by the htree code to indicate that a directory
 130 is being indexed using hashed trees.  It may not be set or reset using
 131 .BR chattr (1),
 132 although it can be displayed by
 133 .BR lsattr (1).
 134 .PP
 135 A file with the 'j' attribute has all of its data written to the ext3
 136 or ext4 journal before being written to the file itself, if the filesystem
 137 is mounted with the "data=ordered" or "data=writeback" options.  When the
 138 filesystem is mounted with the "data=journal" option all file data
 139 is already journalled and this attribute has no effect.  Only
 140 the superuser or a process possessing the CAP_SYS_RESOURCE
 141 capability can set or clear this attribute.
 142 .PP
 143 A file with the 'N' attribute set indicates that the file has data
 144 stored inline, within the inode itself. It may not be set or reset using
 145 .BR chattr (1),
 146 although it can be displayed by
 147 .BR lsattr (1).
 148 .PP
 149 When a file with the 's' attribute set is deleted, its blocks are zeroed
 150 and written back to the disk.  Note: please make sure to read the bugs
 151 and limitations section at the end of this document.
 152 .PP
 153 When a file with the 'S' attribute set is modified,
 154 the changes are written synchronously on the disk; this is equivalent to
 155 the 'sync' mount option applied to a subset of the files.
 156 .PP
 157 A file with the 't' attribute will not have a partial block fragment at
 158 the end of the file merged with other files (for those filesystems which
 159 support tail-merging).  This is necessary for applications such as LILO
 160 which read the filesystem directly, and which don't understand tail-merged
 161 files.  Note: As of this writing, the ext2 or ext3 filesystems do not
 162 (yet, except in very experimental patches) support tail-merging.
 163 .PP
 164 A directory with the 'T' attribute will be deemed to be the top of
 165 directory hierarchies for the purposes of the Orlov block allocator.
 166 This is a hint to the block allocator used by ext3 and ext4 that the
 167 subdirectories under this directory are not related, and thus should be
 168 spread apart for allocation purposes.   For example it is a very good
 169 idea to set the 'T' attribute on the /home directory, so that /home/john
 170 and /home/mary are placed into separate block groups.  For directories
 171 where this attribute is not set, the Orlov block allocator will try to
 172 group subdirectories closer together where possible.
 173 .PP
 174 When a file with the 'u' attribute set is deleted, its contents are
 175 saved.  This allows the user to ask for its undeletion.  Note: please
 176 make sure to read the bugs and limitations section at the end of this
 177 document.
 178 .PP
 179 The 'X' attribute is used by the experimental compression patches to
 180 indicate that the raw contents of a compressed file can be accessed
 181 directly.  It currently may not be set or reset using
 182 .BR chattr (1),
 183 although it can be displayed by
 184 .BR lsattr (1).
 185 .PP
 186 The 'Z' attribute is used by the experimental compression patches to
 187 indicate a compressed file is dirty.  It may not be set or reset using
 188 .BR chattr (1),
 189 although it can be displayed by
 190 .BR lsattr (1).
 191 .PP
 192 .SH AUTHOR
 193 .B chattr
 194 was written by Remy Card <Remy.Card@linux.org>.  It is currently being
 195 maintained by Theodore Ts'o <tytso@alum.mit.edu>.
 196 .SH BUGS AND LIMITATIONS
 197 The 'c', 's',  and 'u' attributes are not honored
 198 by the ext2, ext3, and ext4 filesystems as implemented in the current
 199 mainline Linux kernels.
 200 .PP
 201 The 'j' option is only useful if the filesystem is mounted as ext3 or ext4.
 202 .PP
 203 The 'D' option is only useful on Linux kernel 2.5.19 and later.
 204 .SH AVAILABILITY
 205 .B chattr
 206 is part of the e2fsprogs package and is available from
 207 http://e2fsprogs.sourceforge.net.
 208 .SH SEE ALSO
 209 .BR lsattr (1),
 210 .BR btrfs (5),
 211 .BR ext4 (5),
 212 .BR xfs (5).